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Tuesday, June 17, 2014

The aggressive tiger mosquito, distinguished by its white stripes, can spread chikungunya virus. This mosquito is native to Southeast Asia but has invaded other parts of the world in recent decades, including much of the United States. (Photo by James Gathany/CDC.)

By Carol Clark

As chikungunya virus moves into the Americas for the first time, causing a major outbreak throughout the Caribbean and parts of Central and South America, U.S. health officials are monitoring cases in travelers returning from the affected areas. Imported cases of the mosquito-borne virus have been confirmed in more than a dozen U.S. states, and that number is expected to keep growing.

“Early response is essential,” says Gonzalo Vazquez-Prokopec, a disease ecologist in Emory’s Department of Environmental Sciences who studies how mosquito-borne pathogens move through urban populations. “We need to prepare the country to try to avoid what we suffered with the introduction of West Nile virus 10 years ago.”

Vazquez-Prokopec and Uriel Kitron, chair of Emory’s Department of Environmental Sciences,
have been studying the patterns of vector-borne disease epidemics for
years and are currently working with public health officials in other
parts of the Americas and Africa on chikungunya control efforts.

Kitron will be a featured speaker at a meeting of the NSF-sponsored Urban Climate Institute, hosted by Georgia Tech July 9-10. His talk is titled "Changing Urban Climate and Mosquito-borne Diseases."

The World Health Organization reported the first local transmission of chikungunya in the Western Hemisphere in December of 2013, on the island of Saint Martin. Local transmissions means that mosquitoes in the area have been infected with the virus and are spreading it to people by biting them. Since then, more than 150,000 cases of local transmission have been identified in 17 countries or territories in the Caribbean, Central and South America, according to the Centers for Disease Control and Prevention. Puerto Rico is the only U.S. territory or state that has identified a case of local transmission, the CDC reports.

Chikungunya is rarely fatal but the symptoms can be severe and debilitating, including headache, fever, joint and muscle pain, and joint swelling or rash. While most patients recover within a week, in some people the joint pain can persist for months. Newborns, older adults and people with existing medical conditions are at higher risk for the more severe forms of chikungunya.

The foot of a chikungunya patient in the Philippines shows the characteristic swelling and rash. (Photo by Nsaa.)

There is no vaccine to prevent the disease or medicine to treat infections.
The only way to avoid infection is to prevent mosquito bites by using repellent, window/door screens, and reducing the number of mosquitoes by emptying standing water from containers.

The virus is primarily spread to people by two types of day-time biting mosquitoes: Aedes aegypti and Aedes albopictus. While the former is not common in Georgia, the Aedes albopictus, or Asian tiger mosquito, is pervasive. It is that tiny, infuriating, white-striped pest that crashes countless backyard barbecues, and turns many a relaxing summer session in a hammock into a bloody battle.

“They are like the cockroaches of mosquitoes,” Vazquez-Prokopec says, “perfectly adapted to living in urban areas in close proximity to humans. A house is like a microhabitat for both these species, which can breed in the little bit of water collected beneath an indoor flowerpot.”

The tiger mosquito bites not just people but a range of animals, including squirrels, dogs, deer and birds. The Aedes aegypti, however, which thrives in tropical climates like the Caribbean, feeds solely on human blood.

The Aedes aegypti mosquito is the primary spreader of chikungunya in the current outbreak in the tropical region of the Americas. This mosquito species is an especially efficient spreader of human disease since it only feeds on human blood. (Photo by Muhammed Mahdi Karim.)

“No one has immunity to chikungunya in in the Americas, causing it to spread like a fire and create a real problem for public health,” Vazquez-Prokopec says, noting that in poorer countries fewer homes have air-conditioning, or even window screens, to keep mosquitoes at bay.

Once a mosquito become infected, by taking a blood meal from an infected person, the mosquito can then spread the virus if it bites another person.

“The way the virus is propagating, we expect local transmission of chikungunya to make it to Mexico’s Yucatan Peninsula as early as this summer,” Vazquez-Prokopec says. “It’s just a matter of time.”

He is currently coordinating a chikungunya rapid-response effort for the Yucatan Peninusula. The effort involves health officials from the three states making up the peninsula (Yucatan, Campeche and Quintana Roo) as well as researchers from local universities.
“We want to use our experience researching mosquito-borne disease propagation to help the local authorities try to predict when and where the virus will move,” Vazquez-Prokopec says. “There are two ways of attacking a fire: You try to contain the fire and you also look at where the fire is likely headed to create a buffer to help extinguish it. We know we are in front of a major challenge,” he adds, “but we hope our approach can reduce the chances of a major outbreak occurring in the peninsula.”

Brazil, which reports the highest number of dengue fever cases in the Americas, is another likely destination for serious outbreaks of chikungunya virus, adds Kitron. He is currently in Salvador, Brazil, a city where dengue is highly endemic, collaborating on an entomological study of Aedes aegypti and Aedes albopictus, which are also vectors for dengue.

Chikungunya virus has long been endemic in Africa and parts of Asia. More recent outbreaks have occurred in Europe and countries in the Indian and Pacific Oceans.